Polyacrylaminde (PAM) and hydrolyzed polyacrylamide (HPAM) are common water soluble polymers that have found application in oil field chemicals, paints, paper making, cosmetics, etc. The solution rheology of these materials define their use in these applications. With these polymers, aqueous viscosification or thickening is achieved through a combination of high molecular weight and chain expansion due to repulsion of pendent ionic groups along the polymer chain. High molecular weight polymers are difficult to prepare and dissolve and are also sensitive to shear. Viscosification due to charge repulsion is salt sensitive and thus, these polymers have limited utility in highly saline systems.
Polymerizable esters of acrylic acid or methacrylic acid with alkyl or alkylaryl poly(ethyleneoxy)ethyl alcohols are disclosed in Dickstein U.S. Pat. No. 4,075,411. ##STR1## Trecker, U.S. Pat. No. 3,896,161 and British Pat. No. 828,496. Such monomers have found use in the preparation of stable latexes and special textiles.
Copolymers of base-neutralized acrylic acid and nonionic surfactant acrylates have also found use as thickeners for both aqueous solutions and water/organic liquid emulsions (Koenig and Bryant, U.S. Pat. No. 4,268,641). Improved NaCl tolerance is also taught therein. A liquid composition useful as a thickening agent in polymer latexes, comprising a mixture of solvent and a terpolymer of acrylic acid, an ester of the formula of: ##STR2## and an alkyl acrylate or methacrylate is claimed in U.S. Pat. No. 4,138,381.
The conventional process for recovering water soluble polymers following polymerization is to precipitate the product via addition of a nonsolvent and then dry the product to remove water. Use of this procedure in the preparation, as disclosed in U.S. Pat. No. 4,463,151, of poly(acrylamide-co-nonylphenoxy(ethylene oxy)acrylate) (AM-co-RPEOAc) systems leads to products which are difficult to dissolve, presumably due to strong bonding in these highly associating copolymers. Solutions prepared from the solid polymer have shown enhanced viscosity vs. non-associating polyacrylamide (PAM). However, there was significant concern regarding the degree of polymer degradation which occurs during the lengthy dissolution period (up to four days). Such degradation would be expected to lead to lower solution viscosity. The instant invention discloses an alternative finishing process which yields polymers having improved solution properties as compared to the polymers made by the process of U.S. Ser. No. 454,285.